The present invention refers to a mold for the production of molded skins and molded forms of plastic according to the preamble of claim 1 as well as a device and a method for the production of molded skins and molded bodies from plastic.
Methods for the production of molded skins or molded parts are known under the term rotational casting, rotational sintering or slush casting. In those methods molds are being filled with pourable or also liquid plastic, which is then melted by supplying heat, such that, at the surface of the mold, a thin plastic layer forms. The excess plastic material can subsequently be discarded, before, for example, through further heating, material deposition or a chemical change can take place. After cooling the mold, the completed molded body or the mold skin is taken form the mold. Normally, filling the pourable plastic material into the mold in the form of a powder or granulate is done by means of placing or docking a so-called powder box at the mold with its opening directed downward, and then rotated together with the powder box, such that the plastic powder or granulate falls in the mold and is processed in the above-described manner.
The heat supply can be carried out by means of moving the mold into a hot air chamber. This has however the disadvantage that the heating and cooling of the mold takes a long time, so that the success with the conventional type method is not very high. In addition, when utilizing hot air chambers-or furnaces, the process control, in particular the temperature monitoring is unsatisfactory.
Methods are known that are able to accelerate the production of plastic skins or mold forms by utilizing double-walled molds which are filled with a cooling-or heating medium.
Thus, in DE 41 06 964 C2, a device for the production of molded skins and molded bodies from plastic are described, where a double-walled galvano mold its utilized, which is configured with a multitude of inlet and outlet openings at the rear wall for the heating-and cooling medium, by means of which a fast heating and cooling across the entire surface of the mold is realized. The inlet openings are not necessarily distributed evenly, but in particular embodiments concentration of the heating and cooling medium supply at certain locations is contemplated, which are primarily used to even out differences in the wall thickness in the mold wall that cannot be avoided during production of the mold by galvanic method.
Although, in this manner, varying wall thicknesses can also be realized, yet for a specific production of varying thicknesses in the molded skin, this method is only partially suitable, since on the one hand, the expenditure of the apparatus is very high, and on the other hand the temperature differences on the mold wall are relatively small while at the same time the temperature transitions are undefined and blurry, so that the method is not suitable to realize specific ranges with a lower or higher wall thickness.
With molded skins that are produced by slush casting for the production of instrument dash boards of motor vehicles, the requirements for the wall thickness of the molded skin differs depending on which area is to be covered by the molded skin. Thus, in the air bag area, a molded skin thickness of approximately 1.2 mm is desired, while in the remaining area a thickness of 0.9 mm suffices, which represents a not insignificant potential for material savings if it were possible to realize the varying wall thicknesses.
In the area of the instruments, openings are provided which have to be made in the completed molded skin with an additional work step, which causes, aside from extra work, additional loss of material due to material waste.
Methods are known which can influence the wall thickness of the molded skin or molded bodies through respective control of the cooling- or heating medium or differing heating or oil circulations and thereby their configuration.
Thus, from DE 28 17 030 A1, a method for the production of molded skins is known, where the mold exhibits different areas with different fluid passages with which the production of varying wall thicknesses can be realized. This method has the drawback that it has an enormous apparatus requirement.
There is then still a further demand for a method or a device for the production of molded skins with varying wall thicknesses or even complete recesses in a simple manner.